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weak 5.8 main beam?


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My main beam has developed hair line cracks either side of where the dolphin striker passes through the beam on top. (in fore aft direction)

the thing is the beam is only 3 seasons old and the one before wasn't much older and had the exact same fault.

I have to ask myself if this is an inerrant fault? and what is going on to cause the problem?

any ideas?

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are you talking where the mast step is?

If so if set up correctly there shouldn't be too much load on the main beam it'self in that area ,the dolphin striker should be tensioned up so there is 20mm pre bend in the beam upwards ,if you run out of adjustment the dolphin striker is stretched and needs replacing also if there are any hairline cracks or stress marks on the dolphine striker ,replace it ,you can't be to careful with the dolphin on a 5.8 ,it's the backbone of the whole boat and replacing a $50 - $60 part could save you thousands when you snap your beam and rig, tear your tramp and sails .another problem could be if the nuts either side of the main beam for the dolphin stricker has managed to work their way loose and there's some play there.The way a 5.8 sould be set up there's bugger all load transfered downwards onto the main beam , all (most) of the downwards load should be transfered to the dolphin striker which is why I can't see how your getting stress cracks in your main beam? unless your getting for and aft movement?

good luck


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If the cracks are on top it would seem to point to stress cracking from to much dolphin striker tension, also if the hole through the beam for the dolphin striker bolt was not drilled neatly and any small nicks or burrs smoothed out that would set up stress points for future cracking as has occured. Let us know what you find, (corrosion wise, and tension/ prebend) as I have just bought new beam sections to be fitted

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Yeah the cracks are at the mast base, underneath seems ok.

I run with 10mm prebend, and when sailing the beam looks straight to me, though its a bit hard to tell when your sailing.

the hole at the base of the mast is slogged out, now I didnt fit this beam, so I can only go by what I am told, but the holes were suposedly drilled by the BCC. so you expect them to be reasonably accurate.

with the new beam I am getting the BCC to drill the holes as it will take them far less time, and hopefully far more accurate than I would be.

I did replace the beam of another 5.8 about 5 years ago now, so I will go and check out thats current condition this weekend.

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Originally posted by GRACELAND1216:

Hi Jay,

Are you sure that 20mm pre bend is correct for the front beam, I thought it was more like 6mm and 20 - 30mm for the bridal foil.

Regards Steve.

PS. Have you sold 1606 yet?

might not quite be 20mm but would be fairly close you can definatly see the bend in it!15-20 mm isn't that much over 2m between the hulls!!

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